Method for obtaining a polymer in a solution

ABSTRACT

Process for recovering at least one polymer in solution in a solvent by precipitation by means of a non-solvent introduced gradually into the solution to form the precipitation medium, whereby: in the course of the introduction of the non-solvent into the precipitation medium, there is first a phase separation (into a continuous phase rich in solvent, in which the polymer is dissolved, and into a disperse phase, consisting of droplets rich in non-solvent) and then there is a phase inversion (the continuous phase then becoming the phase rich in non-solvent, and the disperse phase becoming the phase rich in solvent containing the dissolved polymer) the non-solvent is initially introduced into the precipitation medium in liquid form only and in a quantity (Q′) which is not zero but is less than the quantity (Q) required to bring about the phase inversion, and is subsequently introduced into the precipitation medium at least partly in vapour form.

The present invention relates to a process for recovering a polymer insolution.

Polymers are widely used in a variety of forms, primarily in the solidstate. Frequently, however, at a given moment in their existence theyare in solution in a solvent, from which they must then be extracted.Polymer solutions are encountered, for example, at the end of certain(“solution”) polymerization processes, in the course of certainrecycling processes, during the cleaning of certain plants formanufacturing polymer-based articles or paints, etc. These polymers insolution are generally recovered by precipitation with a non-solvent,which may be in liquid form or vapour form or both.

Thus Patent Applications WO 01/23463 and WO 01/70865 in the name ofSolvay describe a process for recycling a plastic (PVC or PVDC) bydissolution in a solvent (MEK or methyl ethyl ketone) and byprecipitation with a non-solvent (water) both in vapour form (to bringabout evaporation of the solvent) and in liquid form (to accelerate theprecipitation of the polymer). This process entails a high energy cost,which is linked to the quantity of vapour employed.

The applicant has found that when non-solvent is added gradually thisprocess proceeds generally as follows. As the non-solvent is added tothe polymer solution to form the precipitation medium, there firstoccurs a phase separation: that is, at a given moment, the systemchanges from a single-phase medium consisting of a solvent-rich phasecontaining the dissolved polymer and a small amount of non-solvent to atwo-phase medium consisting on the one hand of a continuous,solvent-rich phase in which the polymer is dissolved and on the otherhand of a disperse phase consisting of droplets rich in non-solvent.Subsequently, following the addition of a given quantity of non-solvent(which is determined by the phase diagram between solvent and water),there is a phase inversion: that is, the (majority) continuous phasethen becomes the water-rich phase, and the disperse phase is thencomposed of droplets of solvent-rich phase containing the dissolvedpolymer. The injection of vapour into this medium allows the solvent tobe removed substantially by azeotropic distillation.

Surprisingly, although the precipitation of the polymer begins beforethe aforementioned phase inversion, the morphology of the polymerparticles obtained is in fact essentially independent of the steps priorto this inversion and is primarily dependent, in contrast, on theoperating conditions during and after the phase inversion. But movingtowards the composition at phase inversion by injecting vapourunusefully causes the evaporation of a certain quantity of solvent.

To put it another way, the applicant has found that injecting vapour infact has a positive effect on the morphology of the polymer particlesonly during or after the phase inversion, and it is therefore unusefulfor the non-solvent to be in vapour form prior to that stage.

The present invention accordingly provides a process for recovering atleast one polymer in solution in a solvent by precipitation by means ofa non-solvent introduced gradually into the solution to form theprecipitation medium, whereby:

-   -   in the course of the introduction of the non-solvent into the        precipitation medium, there is first a phase separation (into a        continuous phase rich in solvent, in which the polymer is        dissolved, and into a disperse phase, consisting of droplets        rich in non-solvent) and then there is a phase inversion (the        continuous phase then becoming the phase rich in non-solvent,        and the disperse phase becoming the phase rich in solvent        containing the dissolved polymer)    -   the non-solvent is initially introduced into the precipitation        medium in liquid form only and in a quantity (Q′) which is not        zero but is less than the quantity (Q) required to bring about        the phase inversion, and is subsequently introduced into the        precipitation medium at least partly in vapour form.

Optimizing the physical form in which the non-solvent is introduced intothe solution allows a substantial increase to be obtained in theprofitability of the process, without detracting from the quality of theprecipitated polymer obtained.

The polymer whose recovery is targeted by the process according to thepresent invention may be of any kind. It may be a thermoplastic resin oran elastomer, but in any case is a resin that can be dissolved in asolvent and which therefore contains little or no crosslinking. It maybe an unused (or virgin) resin, which has not undergone any melt-formingexcept for possible granulation, or a used resin (production waste orrecycled resin). It may be an apolar polymer, such as a polyolefin and,in particular, an ethylene polymer (PE) or a propylene polymer (PP). Itmay also be a polar polymer such as a halogenated polymer and, inparticular, a vinyl chloride polymer (PVC), a vinylidene chloridepolymer (PVDC) or a vinylidene fluoride polymer (PVDF), etc.; or an EVOHpolymer (a copolymer of ethylene and vinyl alcohol). It may also be amixture of at least two such polymers of the same kind or of differentkind. Good results have been obtained with polar polymers, particularlyhalogenated polar polymers, and very particularly with PVC. By PVC ismeant any homopolymer or copolymer containing at least 50% by weight ofvinyl chloride.

The polymer dissolved in the solvent may include one or more customaryadditives such as plasticizer(s), stabilizer(s), filler(s), pigment(s),etc. The term “compound” is generally used for this type of mixturebased on polymer(s) and additive(s). One advantage of the processaccording to the invention is that it allows these additives to berecovered, i.e. to be coprecipitated with the polymer. Thus, forexample, where the polymer is PVC, it may be plasticized PVC containingone or more plasticizers generally at a level of 75% or less, or even70% or less, or even 65% or less. PVC plasticizers are generally organicesters such as phthalates, adipates, trimellitates, etc., with thegreatest use being made of phthalates and, in particular, DOP (dioctylphthalate). The process according to the invention gives good results inthe case of plasticized polymers (and plasticized PVC in particular).

The solvent (substance able to dissolve the polymer) is preferablyselected from liquids having a solubility parameter (of which adefinition and experimental values appear in “Properties of Polymers”,D. W. Van Krevelen, 1990 edition, pp. 200-202, and in “PolymerHandbook”, J. Brandrup and E. H. Immergut, editors, second edition, p.IV-337 to IV-359) close to that of the polymer to be dissolved and/orhaving strong interactions with said polymer (hydrogen bonding forinstance). The term “close to” generally means “not differing by morethan 6 units”. The solvent is generally an organic solvent, preferably apolar solvent such as MEK (methyl ethyl ketone), which gives goodresults with a large number of polymers and, in particular, withhalogenated polymers such as PVC. The non-solvent for its part ispreferably selected so as to have a solubility parameter which isdifferent from that of the polymer to be dissolved and having no stronginteractions with said polymer. The term “different” generally means“differing by more than 6 units” . It will be appreciated that the termssolvent and non-solvent refer not only to simple substances but also tomixtures of substances. Inorganic liquids are highly suitablenon-solvents, with water being generally the preferred non-solvent (inthe case of polymers which are not water-soluble, obviously) in view ofthe environmental and economic concerns generally involved in industrialprocesses. Moreover, water has the advantage of forming an azeotropewith certain polar solvents such as MEK, which makes it easier to removethe solvent by azeotropic distillation.

The outcome of the above is that in the process according to theinvention the polymer is preferably PVC, the solvent is preferably MEKand the non-solvent is preferably water.

The solutions that can be treated by the process according to thepresent invention have a polymer concentration such that their viscositydoes not interfere with the proper progress of the process (inparticular it is necessary for the non-solvent to be able to begradually mixed and/or dispersed in the solution in order for the two tobe able to interact and for the precipitation to be able to take placeeffectively). In relation to a process where the non-solvent is addedfrom the start in vapour form to the solution (therefore causing thesolvent to evaporate), the process according to the invention makes itpossible to work with higher concentrations of polymer in the solutionsince there is less solvent evaporation. Thus, in the process accordingto the invention, it is possible generally to work with polymer contentsgreater than or equal to 100 g per litre of solvent, even 250 g/l andsometimes even 300 g/l. However, this content generally does not exceed500 g/l, or even 400 g/l. It should be noted that the presence of atleast one dispersant during the addition of non-solvent to the solutiongenerally promotes the mixing/dispersing of the non-solvent in thesolution and therefore makes it possible, generally, to work with moreconcentrated polymer solutions. A dispersant is a substance whichpromotes the dispersion of a discrete phase (which may be formed eitherof liquid droplets or of solid particles) in another phase, thecontinuous phase. The said substance generally acts at the interfacebetween the two phases and it prevents the agglomeration of the discretephase (in other words, it promotes the production of a fine and regulardispersion).

According to the invention, when the polymer is dissolved, non-solventis introduced into the polymer solution, the non-solvent being in liquidform and in a quantity (Q′) which is not zero but is less than thequantity (Q) required to bring about the phase inversion. The quantity(Q), which depends in particular on the nature of the solvent andnon-solvent, on the temperature, on the pressure and, in certain cases,on the quantity of dissolved polymer, is easily determinedexperimentally. All that need be done is to gradually introduce thenon-solvent in liquid form into the solution until phase inversion isobserved (which is readily identifiable for the person skilled in theart) and to measure the quantity of non-solvent added at this point,which is the quantity Q. Good results have been obtained with a quantityQ′ of greater than or equal to 50% (by volume) of the quantity Q, orgreater than or equal to 70%, or even to 90%.

The rate at which the quantity Q′ of non-solvent in liquid form isintroduced generally affects the ASG/average diameter ratio of thepolymer particles obtained. Good results have been obtained when theintroduction time is greater than or equal to 10 minutes or even severaltens of minutes.

According to the invention, when the quantity Q′ has been introducedinto the precipitation medium, the remaining quantity of non-solventrequired to precipitate the polymer is at least partly introduced invapour form. What is meant by this is that at least one fraction of theflow of non-solvent added to the precipitation medium from this time(and generally continuously) is in vapour form. Advantageously thefraction of vapour in this flow is predominant. Preferably all thenon-solvent introduced into the polymer solution after the quantity Q′has been introduced into it is in vapour form.

When the solvent and the non-solvent form an azeotrope, the totalquantity of non-solvent introduced in vapour form is preferablysufficient to allow azeotropic distillation of the solvent. Withparticular preference this amount is sufficient to make the medium afterprecipitation substantially free from solvent. This way of working isparticularly advantageous where the non-solvent is water.

It is not detrimental for the non-solvent introduced into theprecipitation medium (either in liquid or vapour form) possibly tocontain a minority fraction (in weight) of solvent; this is of interestin so far as (as will be set out below for the recycling processes inparticular) a possible downstream step of the process may specificallyprovide such a source of non-solvent, which can therefore be reusedwithout specific purification. Hence, when the non solvent is water,“water” in fact designates an aqueous medium having a majority weightfraction of water (hence, containing more than 50%, even more than 60%and preferably, more than 70% in weight of water). It is preferably purewater or water containing a minority weight fraction of solvent.

According to one version of the present invention the precipitationmedium comprises at least one dispersant. According to an advantageousversion the precipitation medium comprises two different dispersants ofwhich one has a greater affinity for the non-solvent (dispersant I) andthe other has a greater affinity for the solvent (dispersant II).

According to one particularly advantageous version the time at whichthese dispersants are introduced is optimized as a function of theprogress of the precipitation. Thus it is advantageous for thedispersant having the greater affinity for the non-solvent (dispersantI) to be added to the precipitation medium primarily before phaseinversion. For this purpose the said dispersant may be present in thesolution before non-solvent is introduced, or may be introduced by theliquid non-solvent introduced initially.

It is likewise advantageous for the dispersant having the higheraffinity with respect to the solvent (dispersant II) to be added to theprecipitation medium primarily after phase inversion. Optimizing thetype and the time of introduction of the dispersants makes it possibleto optimize the ASG/average diameter ratio of the particles and hence toobtain a compact powder of small particles.

Generally speaking, when precipitation is at an end, the system presentcomprises a suspension of polymer particles in a medium which is rich innon-solvent. The weight proportion of solid particles in this suspensionmay be greater than or equal to 10% without any agglomeration of thesaid particles. In the presence in particular of dispersants asdescribed above, this proportion may even be greater than or equal to25% or even 30%. Introducing the non-solvent in liquid form makes itpossible to obtain more economically (than with vapour) the quantity ofnon-solvent required to give a suspension which is sufficiently dilutedto avoid problems of particle agglomeration.

The polymer particles present in the suspension are collected by anyappropriate means : thermal (evaporation of the solvent, optionally byazeotropic distillation: see above), mechanical (filtration,centrifugation, etc.) or a hybrid form (atomization, for example). Inthe case of temperature-sensitive polymers (such as PVDC, for example)preference will be given to mechanical methods. The particles collectedmay then be washed, dried and treated by any known means prior tostorage, sale and/or use.

The polymer solution to which the present invention is applied may beobtained by any suitable means. However, the dissolving of the polymerin the solvent takes place generally under a pressure at least equal toatmospheric pressure or even at least equal to 1.5 bar. Advantageouslythis pressure does not exceed 10 bar, preferably 5 bar.

The dissolving temperature is generally at least 75° C. or even 100° C.;generally it does not exceed 125° C. or even 110° C.

In the course of this dissolving it may prove to be advantageous to workin an inert atmosphere, under nitrogen for example, in order to avoidany risk of explosion or of degradation of the solvent and/or of thenon-solvent.

During or after the dissolving of the polymer, but before precipitation,it is possible to add one or more additives to the solution. An additivefor the purposes of this version of the invention is any organic orinorganic compound not present in the original plastics, or present in aquantity lower than that which is desired. Possible inorganic additivesinclude inorganic pigments, carbon black, metal powders, nanoparticlesof various kinds, etc. Possible organic additives include organicpigments, stabilizers, oligomers, plasticizers, etc.

The process according to the present invention can be integrated intoany process involving the recovery of a polymer from a solution. Inparticular it may form part of a process for recycling articles based onpolymer(s). The present invention accordingly likewise provides aprocess for recycling at least one article based on at least onepolymer, whereby

-   -   a) if necessary, the article is shredded into fragments with an        average size of 1 cm to 50 cm    -   b) the article or the article fragments is or are contacted with        a solvent able to dissolve the polymer    -   c) the polymer in solution is recovered using the process        described above.

The articles in question may be single-layer or multi-layer solids ofany form (sheet, plate, tube, etc.); they may include a number ofpolymers (only one of which, generally, will then be dissolvedselectively, although the article may likewise serve for the manufactureof an alloy) and also non-polymeric materials (reinforcements, fixings,etc.) which will then be removed before the solution is treated by theprocess described above.

It should be noted that, in the case of articles based on a number ofpolymers, it may prove advantageous to remove the other (or one of theother) polymer(s) before dissolving the polymer it is desired torecover. Thus, for example, if the solvent selected is able to dissolvea number of the polymers in the article, it may prove advantageous firstto eliminate the interfering polymer, for example by means of anothersolvent, which does not dissolve the polymer to be recovered. It shouldbe noted that, when one of the polymers is semi-crystalline, itssolubility may be lowered by an afterbake (that is, residence at atemperature and for a time suitable for obtaining maximumcrystallization). An example of such polymers is given by PVC (anamorphous polymer) and PVDC (a semi-crystalline polymer). Thus, forexample, an afterbake treatment (lasting for 1 h at 70° C. or for 2 daysat 40° C., for example) on a PVC/PVDC complex makes it possible torender the complex insoluble in MEK at 50° C. and hence to dissolve thePVC selectively in MEK at 50° C. (or even at 75° C.) and to apply theprocess as described above to the resulting solution. It should also benoted that the composition of the solvent may be adapted in order todissolve certain polymers of a structure selectively.

In the recycling process described above, the conditions (pressure,temperature, stirring, etc.) in which the polymer is dissolved and inwhich, optionally, non-polymeric elements or elements based on aninterfering polymer are separated before precipitation (by filtration,prior dissolution, etc.) will be optimized by any means known to theperson skilled in the art. Teaching useful for this purpose is given inApplications EP 945481, WO 01/23463 and WO 01/70865 in the name ofSolvay, and is incorporated by reference into the present application.

A recycling process of this kind has been successfully applied toarticles comprising PVC.

A major advantage of such a recycling process is that it is able tofunction in a closed loop (either continuously or batchwise, but withquasi-total recirculation of the liquid phase, with the exception oflosses due in particular to adsorption on the polymer particlesobtained), without generating refuse. Indeed, the liquid medium obtainedafter precipitation and separation of the polymer particles, whichconsists primarily of non-solvent (possibly containing the dispersants),may be recycled, where appropriate by means of appropriate treatment.This treatment may consist in one or more distillations, flocculations,decantations, washings, etc., and in combinations of these treatments.Similarly, when the solvent has been removed from the precipitationmedium by azeotropic distillation with the non-solvent, the vapoursresulting from this distillation may be condensed and may constitute aliquid phase which can be treated as described above. This treatmentpreferably includes at least one decantation and, in that case, it isadvantageous for the said decantation to proceed at least partly in thepresence of a phase separation agent. Thus where two or moredecantations take place (in parallel or in series) it is advantageousfor at least one of them to take place in the presence of a phaseseparation agent. A phase separation agent is a substance which promotesthe decantation (in other words, the formation of two phases one rich insolvent, the other rich in non-solvent) of the condensed vapours fromthe azeotropic distillation.

It should be noted, however, that the applicant has found that thepresence of a phase separation agent in the precipitation medium (asrecommended in application WO 01/70865) at the time of phase inversionand thereafter (that is, during the steps which determine the morphologyof the polymer particles) generally had an adverse effect on the saidmorphology. Moreover, in the case of a closed loop process utilizing aphase separation agent, it is advantageous for the solution of polymerto be precipitated to be substantially free of phase separation agent(that is, to contain not more than a few % by weight thereof). However,the presence of this phase separation agent during the above mentioneddecantation treatments is favourable. Consequently, according to oneparticularly advantageous version of the recycling process as describedabove, the said process is a closed loop process in which the solventand the non-solvent are regenerated at least in part by decantation, andin which a phase separation agent is present at least in part during thesaid decantation but is absent during the precipitation of the polymer.For this to be so, the agent is substantially removed from the liquidmedium (primarily solvent) before the polymer is precipitated and theagent is added again to the liquid medium (media) obtained from theprecipitation before or during its(their) decantation. The phaseseparation agent may be removed by any means known for this purpose;distillation provides good results when the boiling point of this agentis substantially different from that of the solvent and of thenon-solvent.

One such variant is illustrated non-limitatively by FIG. 1, whichrepresents diagrammatically a specific recycling process applied to PVC.

In this process, PVC in particulate form (1) and a solvent primarilycontaining MEK (2) are introduced at the dissolving step (D). This givesa solution of PVC (3) which is introduced in the precipitation step (P)together with a non-solvent primarily containing water (4). Thisnon-solvent is introduced in the precipitation step (P) first of all insolely liquid form (4′) and subsequently, by means of a vaporization(V), in vapour form (4″). The flow rate (4′) is calculated in order toinject into the precipitation (P) a quantity of water Q′ which is lessthan the quantity Q required to bring about the phase inversion. Theflow rate (4″) for its part is calculated in order to allow completeprecipitation of the PVC and complete removal of the MEK from theprecipitation medium by azeotropic distillation. At the end of theprecipitation step (P) the media present comprise

-   -   on the one hand, a suspension of PVC in water (5), which is        subjected to a solids/liquids separation (S) to give particles        of PVC (6) and water (7)    -   on the other hand, vapours obtained from the azeotropic        distillation of water/MEK (8).

These vapours (8) are subjected to condensation (C) to form an unstableliquid (8′) which is subjected to decantation (D1), at the end of whicha water-rich phase (9) and an MEK-rich phase (10) are obtained. Thislatter phase (10) is in turn subjected to decantation (D2) in thepresence of hexane (11) to give a water-rich phase (12) and an MEK-richphase (13) containing hexane and a little water.

The water-rich phase (12) is combined with the water (7) obtained fromthe separation step (S) and with the water-rich phase (9) obtained fromthe decantation (D1) in order to form the flow of water (4) used for theprecipitation (P). The MEK-rich phase (13) is subjected to adistillation (DST) which makes it possible on the one hand to regeneratethe hexane (11), which is recycled to the decantation (D2), and, on theother hand, to obtain MEK, which now contains no more than a few % ofwater and hexane, and which constitutes the solvent (2) used for thedissolving (D). The fact that this solvent contains a small amount ofhexane is not a problem since, although this hexane is present at theprecipitation step (P), it is removed from the medium before the phaseinversion (since the quantity of liquid water Q′ is less than thequantity of water Q required for phase inversion, this quantity Q isattained by injecting steam, which has the effect of evaporating thehexane, the more volatile compound of the water/MEK/hexane mixture).

In the process according to FIG. 1 the phase separation agent issubstantially removed from the liquid medium obtained from thedecantation (D2). This way of working makes it possible, through the useof a solvent buffer (that is, a “double” of the solvent which is intreatment (decantation/distillation) while a manufacturing cycle takesplace, and which is used during the following cycle, while the usedsolvent from the preceding cycle is treated in its turn), not to prolongthe duration of the manufacturing cycles (or batches). Alternatively thephase separation agent may be removed between the dissolving step (D)and the precipitation step (P). This alternative, however, is lessadvantageous, because

-   -   distilling the polymer solution may affect the morphology of the        polymer particles that will be obtained    -   the cycle time (duration of one batch) is prolonged, since the        use of a solvent buffer is not possible.

The advantage of the first alternative may be extended more generally toany recycling process as described above provided that it operates in aclosed loop with at least partial regeneration of the solvent and of thenon-solvent by decantation in the presence (at least in part) of a phaseseparation agent, that the phase separation agent has a greater affinityfor the solvent than for the non-solvent, and that it is substantiallyremoved from the solvent before the polymer is dissolved. By“substantially removed” is meant that at most a few % (by weight) ofphase separation agent may be left in the solvent and/or thenon-solvent.

The present invention is also illustrated non-limitatively by thefollowing examples

Preliminary Test: Determining the Quantity Q

Liquid water was added gradually to PVC solutions at variousconcentrations, temperatures and pressures and it was observed that thephase inversion took place in each case when the quantity of water wasapproximately equivalent (by volume) to the quantity of MEK employed.

REFERENCE EXAMPLE 1 AND EXAMPLES 2 TO 4 (INACCORDANCE WITH THEINVENTION)

In each of these tests 333 g of plasticized PVC (PVC of Kw 71 with 25%by weight of DOP (dioctyl phthalate)) were dissolved (in one hour at 75°C. under atmospheric pressure and with a helical stirrer rotating at 250revolutions/minute) in a given quantity of solvent (S) which is eitherMEK (M) in pure form or a solvent containing MEK, water and hexane (WH:)in quantities which are a function of the target concentration (seetable below).

These solutions were then brought to 50-55° C., the pressure was reducedto 600 mbar and liquid water was introduced in a given quantity (Q′<Q)and with a given introduction time (t). Thereafter vapour was injectedat a rate of 3.6 kg/h in a quantity (Q″) at least sufficient to bringabout total precipitation of the PVC.

The solvent was recovered by condensation, for re-use. The PVC compoundcollected was in suspension in water. It was filtered on a 125 μm metalfilter and was subsequently dried in an oven under vacuum (0.2 bara) at80° C. for 5 hours. The powder of precipitated PVC compound wassubsequently screened on a 1 mm sieve before use, and thereafter its ASGand its average diameter were measured and the ASG/average diameterratio was calculated, which constitutes an indicator of the quality ofthe PVC particles obtained.

The detail of these tests and the results obtained are given in Table 1.

It is observed that

-   -   despite the injection of a quantity of vapour significantly less        than in reference example R1, the examples in accordance with        the invention allow particles of similar or even greater quality        to be obtained    -   an introduction time of the order of 10 minutes for the starting        liquid allows particles to be obtained whose quality is better        than for a time of 2 minutes (Example 3 relative to Example 2).

EXAMPLES 5 To 8 (IN ACCORDANCE WITH THE INVENTION

The procedure of Examples 1 to 4 was repeated but on a larger scale andwith the quantities of PVC dissolved being varied in order to give theweight concentrations which feature in Table 1, which also contains thedetail of the tests and the results obtained.

In test 7 a less plasticized PVC was used (PVC of Kw 71 containing 20%by weight of DOP).

It is observed that:

-   -   the increase in the plasticizer concentration has an adverse        effect on the quality of the PVC particles obtained (Example 6        relative to Example 7)

the presence of hexane at the time of phase inversion also has anadverse effect on the quality of the PVC particles obtained (Example 8relative to Example 5). S Type of [PVC]_(sol) Q′ T Q″ ASG Dav Ex. (kg)S(l) = Q S (wt. %) (l) Q′/Q (min) (l)* (g/cm³⁾ (μm) ASG/Dav R1 3330 4.16MWH 9.1 0 0   — 1.50 458 503 0.9 2 2220 2.8 M 15 1.5 0.54  2 0.50 399384 1.0 3 2220 2.8 M 13 1.5 0.54 10 0.50 519 339 1.5 4 1665 2.1 M 17 1.50.71 10 1.00 541 303 1.8 5  160 200 M 17 100 0.50 30 140 677 375 1.8 6 130 163 M 20 100 0.61 30 110 659 379 1.7 7  130 163 M 20 100 0.61 30140 728 224  3.25 8  160 200 MWH 17 100 0.50 30 140 625 501  1.25

1-10. (canceled)
 11. A process for recovering at least one polymer insolution in a solvent which comprises precipitating by means of anon-solvent introduced gradually into the solution to form theprecipitation medium, wherein: in the course of the introduction of thenon-solvent into the precipitation medium, there is first a phaseseparation (into a continuous phase rich in solvent, in which thepolymer is dissolved, and into a disperse phase, consisting of dropletsrich in non-solvent) and then there is a phase inversion (the continuousphase then becoming the phase rich in non-solvent, and the dispersephase becoming the phase rich in solvent containing the dissolvedpolymer) the non-solvent is initially introduced into the precipitationmedium in liquid form only and in a quantity (Q′) which is not zero butis less than the quantity (Q) required to bring about the phaseinversion, and is subsequently introduced into the precipitation mediumat least partly in vapour form.
 12. The process according to claim 11,wherein the polymer is PVC, the solvent is MEK (methyl ethyl ketone) andthe non-solvent is water.
 13. The process according to claim 11, whereinthe quantity Q′ is greater than or equal to 50% (by volume) of thequantity Q.
 14. The process according to claim 11, wherein theintroduction time of the quantity Q′ into the precipitation medium isgreater than or equal to 10 minutes.
 15. The process according to claim11, wherein all the non-solvent introduced into the precipitation mediumafter the quantity Q′ has been introduced into it is in vapor form. 16.The process according to claim 1, wherein the solvent and thenon-solvent form an azeotrope and the total quantity of non-solventintroduced in vapor form is sufficient to allow the azeotropicdistillation of the solvent.
 17. The process according to claim 11,wherein the precipitation medium comprises two different dispersants ofwhich one has a greater affinity for the non-solvent (dispersant I) andthe other has a greater affinity for the solvent (dispersant II). 18.The process according to claim 16, wherein the precipitation mediumcomprises two different dispersants of which one has a greater affinityfor the non-solvent (dispersant I) and the other has a greater affinityfor the solvent (dispersant II).
 19. A process for recycling at leastone article based on at least one polymer which comprises: a) optionallyshredding the article into fragments with an average size of 1 cm to 50cm, b) contacting the article or the article fragments with a solventable to dissolve the polymer and c) recovering the polymer in solutionusing a process according to claim
 1. 20. The process of recyclingaccording to claim 19, which is a closed loop process in which thesolvent and the non-solvent are regenerated at least in part bydecantation, and wherein a phase separation agent is present at least inpart during the said decantation but is substantially absent during theprecipitation of the polymer.
 21. The process according to claim 20,wherein the phase separation agent has a greater affinity for thesolvent than for the non-solvent and is substantially removed from theregenerated solvent before the polymer is dissolved.